International Journal of Marine Science, 2025, Vol.15, No.1, 15-27 http://www.aquapublisher.com/index.php/ijms 23 genetic variation means more possible phenotypic combinations in the population, thus having a greater chance of genotypes adapted to new environmental conditions such as temperature rise, salinity changes, or new pathogens (Puritz et al., 2022). Studies have shown that oyster populations with high genetic diversity tend to be more resistant to disease outbreaks or extreme climate events and recover faster after disasters. Genetic connectivity is one of the key mechanisms to maintain diversity. Through gene flow, alleles in different regional populations can be recombined, thereby increasing genetic variation locally. In the context of habitat fragmentation, promoting moderate connectivity among populations can help alleviate the decline in diversity caused by inbredness and genetic drift. In management practice, this means avoiding over-isolating oyster populations. A Korean Pacific oyster study is an example: they strengthened the local population by introducing Japanese oysters with different genetic backgrounds, and the population diversity metrics created were increased by about 10%~15%, and achieved a 4-fold increase in effective population size (Hughes et al., 2019). However, attention should also be paid to balance "genetic rescue" and "external gene invasion". In addition to natural population protection, the management of genetic diversity should also be paid attention to in breeding and recovery situations. During artificial breeding, as many parents as possible should be used and their contributions should be balanced to prevent the effective population size of the offspring population from being too small. Experts point out that aquaculture often tends toward a few high-yield lines, which will lead to a significant decline in genetic diversity and will need to be alleviated by rotating broodstock or introducing wild bloodlines. For restoration projects, such as artificial reef building, it is necessary to ensure that the young oysters released have sufficient genetic variation to adapt to the on-site environment, otherwise the restoration population may be difficult to maintain itself. 6.2 Connectivity protection strategies in the context of habitat fragmentation With coastal development and environmental degradation, many oyster habitats are fragmented and the risk of populations being isolated from each other increases. In this context, specialized protection strategies need to be developed to maintain or restore genetic connectivity networks. The first is to optimize the protection space pattern. Based on the knowledge of existing oyster reefs and population distributions, a systematic planning approach can be used to establish a network of interconnected protected areas rather than an isolated single area. Research shows that controlling the protection zone spacing within the average diffusion distance of oyster juveniles helps ensure sufficient genetic exchange between protected zones. For example, when planning for the recovery of native oysters in Europe, NORA recommends establishing multiple recovery points within a range of dozens of kilometers, so that oyster juveniles in one area can achieve genetic exchange through phased diffusion. For those areas that are "functionally extinct", genetic connectivity can be gradually restored from zero to near-natural state through continuous reef construction in adjacent seas. Secondly, the construction of habitat corridors is also a feasible strategy. Under natural conditions, oyster reefs are often distributed in chains along the estuary bay, which itself acts as a "corridor" for gene flow. If these continuous belts are destroyed, artificial construction of alternative corridors can be considered. In terms of controlling human activities, it is also necessary to focus on maintaining connectivity (Powers, 2025). It should be pointed out that in the case of severe habitat fragmentation, sometimes auxiliary migration is also a last resort. When both populations are geographically close to isolation but both face the risk of extinction, artificial transfer of some individuals can introduce new genetic variations, reduce inbredness and improve overall survival opportunities. This is called "genetic rescue" and has successful cases in other species. However, the differences in adaptability of the two groups must be carefully evaluated when implementing oysters to avoid causing genetic contamination or disease transmission. 6.3 Genetic interference and management measures of wild and breeding populations Because oysters have both fishery and breeding values, it is inevitable that there will be mutual influence between wild populations and breeding populations, causing potential genetic interference problems. It is mainly reflected in two aspects: First, artificial selection and inbreding during the breeding process may cause the genetic structure
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